Method and apparatus for surface hardening an elongated workpiece having a spade-shaped portion



Aug. 29, 1967 G. H. LEDL ETAL 3,33,!5g I METHOD AND APPARATUS FOR SURFACE HARDENING AN ELONGATED WORKPIECE HAVING A SPADE-SHAPED PORTION Filed June 22, 1965 INVENTORS. GEORGE M. MUCHA 8| GEORGE H. LEDL Wilma/lady ATTORNEYS United States Patent METHOD AND APPARATUS FOR SURFACE HARD- ENING AN ELONGATED WORKPIECE HAVING A SPADE-SHAPED PORTION George H. lLedl, South Russell, Geauga, and George M. Mucha, Parma Heights, Cuyahoga, Ohio, assignors to The Ohio tCrankshaft Company, Cleveland, Ohio, a corporation of Ohio Filed June 22, 1965, Ser. No. 465,857 11 Claims. (Cl. 148-146) This invention pertains to the art of induction heating and, more particularly, to a method and apparatus for surface hardening an elongated workpiece having a spadeshaped portion, with the irregular surface of the workpiece being heated inductively and then quench hardened.

The present invention is particularly applicable to surface hardening an axle shaft having a spade-shaped connecting end, and it will be described with particular reference thereto; however, it will be appreciated that the invention has much broader applications and may be used to surface harden various elongated workpieces having both a shaft portion or portions and a spade-shaped portion.

The term spade-shaped as used herein refers to a flattened portion along the axis of an elongated workpiece where the flattened portion has a first transverse dimension generally the same as the transverse dimension of the rest of the workpiece and a second transverse dimension substantially larger than the transverse dimension of the rest of the workpiece. In other words, an elongated workpiece with a spade-shaped portion will have a profile from one direction where the spade-shaped portion does not project outwardly to any great extent from the workpiece proper and a profile in a perpendicular direction where the spadeshaped portion projects a substantial distance from the workpiece proper.

Surface hardening of elongated workpieces, such as axle shafts for motor vehicles, is generally accomplished by an induction heating apparatus including an inductor having a workpiece receiving opening and a quenching unit having a workpiece receiving passage, with the opening and passage being generally aligned. The axle is moved slowly and successively through the inductor and the quenching unit. To assure uniformity of the hardness pattern on the surface of the workpiece, the axle shaft is usually rotated as it moves through both the inductor and the quenching unit. Since the surface of the axle shaft to be hardened is generally cylindrical, the opening in the inductor and the passage in the quenching unit are circular in shape and have a diameter only slightly larger than the diameter of the cylindrical surface to be hardened.

Heretofore, the diameter of the opening through the inductor has been accurately dimensioned so that the air gap between the rotating cylindrical surface being heated and the inductor provided optimum magnetic coupling between the flux field created by the inductor and the cylindrical surface of the rotating axle shaft. This air gap remained substantially uniform since the rotating axle shaft was cylindrical and the inductor opening was circular. In the art of induction heating, it was believed that thisuniformity of the air gap between the inductor and the rotating shaft was required to provide proper heating of the shaft before it was quench hardened.

Certain axle shafts for motor vehicles have been designed and are now in use which could not, heretofore, be inductively heated. These axle shafts include a shaft portion and a spade-shaped connecting end both of which require surface hardening to prevent premature failure of the axle shaft during use. With a spade-shaped connecting end, an inductor having a circular workpiece receiving opening generally matching the shaft portion of the axle shaft can not be utilized for inductively heating the spadeshaped portion of the axle shaft. With the preselected air gap in the inductor, the spade-shaped portion can not pass through the circular inductor because the large transverse dimension of the spade-shaped portion can not be accommodated by the small circular opening in the inductor.

Attempts were made to inductively heat the shaft portion of this axle shaft separate from the spade-portion; however, this separate heating of the two portions of the axle shaft resulted in an uneven heating pattern in the area betwen the separately heated portions. This uneven heating pattern caused premature failure of the axle shaft. Consequently, these axle shafts with spade-shaped connecting portions were surface hardened by carburizing the surface, and then quenching the axle shaft by dipping the same in a quenching medium. Although this proved somewhat expensive and resulted in substantial distortions of the axle shaft, it has heretofore been the only method of surface hardening an axle shaft with a spade-shaped connecting end in a manner which would allow sufficient surface hardening of the shaft for use in a motor vehicle.

The present invention is directed toward a method and apparatus for surface hardening an axle shaft having a spade-shaped connecting end or any elongated workpiece having a shaft portion and a spade-shaped portion which method and apparatus utilizes progressive induction heating and quenching of all surfaces of the workpiece in a continuous operation.

In accordance with the present invention, there is provided a method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft portion and a spade-shaped portion. This method comprises the steps of providing an inductor having a workpiece receiving opening generally matching the spade-shaped portion of the workpiece; providing a quenching unit with a workpiece receiving passage which will allow passage of the spade-shaped portion of the workpiece; moving the workpiece successively through the opening and the passage, energizing the inductor as the workpiece is moved through the opening, directing quenching fluid from the quenching unit as the workpiece is moved through the passage and rotating the workpiece about the axis only when the shaft portion of the workpiece is within the energized inductor.

In accordance with another aspect of the present invention, there is provided an apparatus for surface hardening a steel workpiece with a longitudinal axis and comprising a shaft portion and a spade-shaped portion. This apparatus comprises an inductor having a workpiece receiving opening generally matching the spade-shaped portion of the workpiece, means for selectively energizing the inductor, a quenching unit with a workpiece receiving passage which will allow passage of the spade-shaped portion of the workpiece, means for selectively directing a quenching fluid from said quenching unit inwardly of the passage, means for aligning the spade-shaped portion with the opening of the inductor, means for moving the workpiece successively through the opening and through the passage, and means for rotating the workpiece about its axis only when the shaft portion of the workpiece is within the opening of the inductor.

By providing the inductor with a workpiece openin matching the spade-shaped portions of the workpiece, the spade-shaped portions of the workpiece can understandably be inductively heated; however, under all heretofore recognized principles of induction heating, it would be impractical, if not impossible, to inductively heat the shaft portion of the workpiece with this same inductor. The opening of the inductor is contoured to match only the spade-shaped portion of the workpiece. The magnetic coupling between the inductor opening and the cylindrical shaft portion of the workpiece would appear to be inappropriate for effectively heating the shaft portion of the workpiece. However, it has been found that a uniform heating pattern can be accomplished in all surface areas of the workpiece by moving the spade portion of the workpiece through the inductor without rotation and, as soon as the spade-shaped portion is passed from the inductor, rotating the workpiece while the shaft portion of the workpiece is within the mismatched opening of the inductor. This apparatus substantially overcomes all prior difficulties in surface hardening this particular irregularly shaped, elongated workpiece and results in a uniform hardness pattern on the surfaces of the workpiece.

The primary object of the present invention is the provision of a method and apparatus for surface hardening an elongated workpiece having a shaft portion and a spadeshaped portion which method and apparatus uses induction heating and provides a somewhat uniform hardness pattern in both the shaft and spade-shaped portions of the workpiece.

Another object of the present invention is the provision of a method and apparatus for surface hardening an elongated workpiece having a shaft portion and a spadeshaped portion which method and apparatus utilizes a single inductor for progressively heating both the shaft and spade-shaped portions of the workpiece.

Still another object of the present invention is the provision of a method and apparatus for surface hardening an elongated workpiece having a shaft portion and a spade-shaped portion which method and apparatus utilizes a single inductor for progressively heating both the shaft and spade-shaped portions of the workpiece with the workpiece being rotated only when the shaft portion of the workpiece is within the inductor.

These and other objects and advantages will become apparent from the following description used to illustrate the preferred embodiment of the invention as read in connection with the accompanying drawing in which:

FIGURE 1 is a side elevational view showing, somewhat schematically, the preferred embodiment of the present invention;

FIGURE 1A is an enlarged, partial pictorial view illustrating a workpiece having a shaft portion and a spadeshaped portion;

FIGURE 2 is a side elev-ational view similar to FIG- URE 1 illustrating the preferred embodiment of the present invention at a different operational position and a slight modification of the embodiment shown in FIGURE 1;

FIGURE 3 is an enlarged cross-sectional view taken generally along line 3-3 of FIGURE 1; and

FIGURE 4 is an enlarged schematic view taken generally along line 44 of FIGURE 1.

Referring now to the drawing wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, FIGURES 1 and 2 show an apparatus for surface hardening an elongated workpiece including a shaft portion and a spade-shaped portion. In accordance with the illustrated embodiment of the present invention, apparatus A is utilized for surface hardening an axle or axle shaft B, best shown in FIGURE 1A. The axle includes a shaft portion having a diameter x and a connecting end or spade-shaped portion 12 having a large transverse dimension y which is substantially larger than diameter x of shaft portion 10. In accordance with the illustrated embodiment, the large dimension y is more than three times greater than diameter x; however, it will be appreciated that various ratios of dimension y to diameter x are within the contemplation of the present invention. Portion 12 also includes a small transverse dimension z which is the same as or slightly smaller than the diameter x of shaft portion 10. It is appreciated that the dimension z could also be slightly larger than the diameter x; however, this dimension cannot be substantially greater than the diameter x. Although the axle B, as illustrated, includes a spadeshaped portion 12 at the end of shaft portion 10, it should be appreciated that the present invention would also be applicable for surface hardening an elongated workpiece wherein the spadeaportion 12 was intermediate two shaft-portions extending in opposite directions. Other variations of this general concept can easily be envisioned.

Referring now in more detail to apparatus A, the apparatus includes an inductor 20 having a plurality of turns, three turns being shown, and a workpiece receiving opening 22, best shown in FIGURE 3. The turns of the inductor are connected by leads 24, 26 onto a power source, schematically represented as generator 28. A schematically represented switch 30 is illustrated for selectively energizing the inductor 20. Although the switch is shown in lead 24, it is appreciated that the inductor 20 may be energized selectively by various arrangements, such as a switch to the input side of the generator 28 or a switch within the field circuit of the generator. Referring now to FIGURE 3, the opening 22 of inductor 20 is generally rectangular and generally matches the outer periphery or dimensions y and z of spade-shaped portion 12. Essentially, the dimensions of the opening 22 can be expressed as (x+2K and (y+2K with K and K being normal air gap constants for spacing an inductor from a workpiece. Being more general, the large dimension of the rectangular opening 22 is determined by the dimen sion y of the spade-shaped portion 12, and the small dimensions of the opening 22 is determined by the diameter of the shaft portion x. This small dimension is also determined by the dimension z of the spade-shaped portion 12 because this dimension is substantially the same as the diameter x, as previously explained.

In accordance with the invention, induction heating of the workpiece or axle B is accomplished by moving the spade-shaped portion of the workpiece through opening 22 while the inductor is energized and without rotating the workpiece. After the spade-shaped portion 12 passes through the inductor, the shaft-portion 10 is inductively heated by rotating the workpiece about its longitudinal axis and moving the shaft portion 10 longitudinally through the energized inductor 20. To accomplish this heating operation, and the subsequent quenching of the heated workpiece or axle B, reference is again made to the details of apparatus A as shown in FIGURES 1 and 2.

Apparatus A includes aligned centers 40, 42 secured onto a frame 44 supported by appropriate means, not shown, for reciprocal movement in a direction parallel with the axis of axle B. The upper center 40 is secured onto the output shaft of a motor 46, which is energized by leads 46a, 46b to rotate the axle B. The lower center 42 is secured onto a pneumatically actuated cylinder 48. Axle B is loaded between centers 40, 42 by first retracting center 42, placing the workpiece in the position illustrated in FIGURE 1, and then forcing the center 42 against the spade-shaped portion 12 by introducing fluids, such as air, into cylinder 48. With the axle between the centers, movement of frame 44 downwardly will progress the axle through the opening 22 in the inductor 20.

Although a variety of structures could be utilized for moving the frame 44, in accordance with the illustrated embodiment of the invention, a threaded nut 50 is fixedly secured onto the frame 44 in a position to coact with a lead screw 52 which can be rotated by motor 54. As best shown in FIGURE 2, the output shaft for motor 54 is rotated in a direction that will move frame 44 downwardly when the motor is energized by leads 54a, 54b. In like manner, movement of the frame 44 upwardly is accomplished by energizing motor 54 by leads 54a, 540. A switch 56 selectively connects the proper leads of reversible motor 54 onto power leads L L to provide, selectively, the proper movement of the frame 44.

Below inductor 20, there is provided a quenching unit 60 having a central workpiece receiving passage 62. The diameter of the passage is greater than the large dimension y of the spade-shaped portion 12 so that portion 12 may move through the quenching unit while it is rotating or while it is not rotating. In accordance with the illustrated embodiment of the invention, the quenching unit 60 includes an internal fluid passageway 64 having a plurality of radially directed orifices 66. A conduit 68 is connected with passageway 64 and with quench fluid supply 70 so that quenching fluid may flow from the supply 70 through conduit 68 into the passageway 64. Thereafter, the quenching fluid flows from orifices 66 in a radially inward direction to impinge upon and, thus, quench the previously heated portions of axle B. The quenching supply 70 is actuated when current is supplied through control lines 70a, 70b, in a manner to be hereinatfter described.

Referring again to the frame 44, the frame is provided with a cam 80 having spaced shoulders 82, 84. These shoulders actuate a switch 86 by contacting switch arm 88. When the switch 86 is closed by engagement of arm 88 with cam 80, leads 70a, 70b of quench supply 70 and leads 46a, 46b of motor 46 are connected in parallel with each other and with leads 54a, 54b of motor 54. Consequently, when switch 86 is closed and switch 56 is connected to move the frame in a downward direction, motor 46 is actuated to rotate the axle and quench supply 70 is actuated to direct a quenching fluid toward the previously heaed workpiece.

Before portion 12 of the axle B can pass into opening 22 of inductor 20, the portion 12 must be properly ligned. This may be accomplished manually or by a variety of mechanisms. For illustrative purposes only one aligning mechanism 90 is schematically shown in FIGURES 1 and 4. This mechanism includes a cylinder 92 having an operating rod 94 adapted to move an aligning head 96 toward and away from axle B. Aligning head 96 is best shown in FIGURE 4 and it includes spaced aligning legs 100, 102 diverging outwardly from a nest 104 which generally matches the periphery of portion 12. Consequently, as rod 94 forces head 96 toward the workpiece, the legs 100, 102 rotate the portion 12 until the portion slides into thenest 104. In this position, the portion 12 is accurately aligned with opening 22 of the inductor 20. If the portion 12 of axle B is perpendicular to its desired aligned position, as shown in FIGURE 4, there is a possibility that the portion 12 would jam against the diverging legs 100, 102. To prevent this, leg 102 is provided with an inwardly extending camming finger 106 which will rotate the portion 12 from the perpendicular position so that the legs 100, 102 can accurately guide the portion 12 into nest 104. It is appreciated that various other structures could be utilized for aligning the portion 12 with the opening 22.

In operation the axle B is positioned between centers 40, 42, as shown in FIGURE 1, in a manner previously described. Thereafter, switch 56 is shifted to the solid line'position which energizes motor 54 to rotate lead screw" 52 in the proper direction so that frame 44 progres'ses downwardly. Aligning mechanism 90 has previously aligned portion 12 with opening 22; therefore, the portion 12 is moved into the inductor 20. At this time, or prior thereto, switch 30 is closed to energize inductor and the inductor heats the portion 12 by known induction principles. Axle B can be held stationary while the portion 12 is being heated. This is accomplished by opening switch 56. Although this procedure has proven satisfactory in use, it is also within the contemplation of thepresent invention to slowly progress the portion 12 through the energized inductor 20 without holding it stationary. After the inductor 20 has heated the portion 12, the frame is moved further in a downward direction so that theportion 12 moves through the quenching unit 60. As soon as the portion 12 passes through the quenching unit 60, the switch 86 is closed. This actuates motor 46 to commence rotation of the workpiece B and, simultaneously, actuates the quenching supply. This automatically quenches the previously heated portion 12 and 6 quenches the shaft portion 10 of axle B as it is heated by the inductor 20. During heating of the shaft portion 10, the workpiece is being rotated by the motor 46.

It should be appreciated that the quench supply 70 can be actuated before rotation of motor 46 actually starts. In practice, this is done. For this reason, quenching of the portion 12 takes place immediately as it progresses through the passage 62. The rotation of the axle does not start until the portion 12 moves through passage 62. If rotation of the axle commences before the portion 12 passes through the quenching unit 60, the paddle effect of the rotating portion 12 could splash the quenching fluid upwardly against the inductor and the workpiece being heated. This would cause certain defects in the heating operation.

In essence, the present invention involves the utilization of an inductor 20 best adapted for inductively heating the portion 12 of the axle with the portion 12 of the axle passing through the inductor before rotation of the axle commences. The rotation of the axle while shaft portion 10 is within the inductor provides a uniform heating of the shaft 10 even though the inner contour of the inductor is not of the type which would conceivably produce a suflicient magnetic coupling to efficiently heat the shaft portion 10.

As mentioned above, rotation of the workpiece, in practice, is not started until the portion 12 passes through the quenching unit 60 because the rotating portion 12 would tend to splash the quenching fluid upwardly into the heating area of inductor 20. If it is desired to start rotation of the workpiece immediately after portion 12 passes from the inductor, it is possible to do this by providing splash shields 110, 112, shown in FIGURE 2. These splash shields are adapted to move inwardly as portion 12 passes so that the portion 12 may be rotated While within passage 62 of the quenching unit 60. These splash shields prevent upward splashing of the quenching fluid toward the inductor. It is appreciated that the splash shields preferably are constructed from a non-magnetic material, such as an electrical insulator.

If the workpiece being heated has a spade-shaped portion intermediate two shaft portions, the workpiece is rotated as the first shaft portion is heated, is not rotated as the spade-shaped portion is heated and is, then, again rotated as the second shaft portion is heated. Variations of this process can be made to accommodate two or more spade-shaped portions on the same workpiece.

The present invention has been described in connection with one structural embodiment; however, it is ap preciated that various structural changes may be made in this embodiment without departing from the intended spirit and scope of the present invention as defined in the appended claims.

Having thus described our invention, we claim:

1. A method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft portion and a spade-shaped portion, said method comprising the steps of: providing an inductor having a workpiece receiving opening generally matching said spade-shaped portion; providing a quenching unit with a workpiece receiving passage which will allow passage of said spadeshaped portion; moving said workpiece successively through said opening and said passage; energizing said inductor as said workpiece is moved through said opening; directing quenching fluid from said quenching unit as said workpiece is moved through said passage; and rotating said workpiece about said axis only when said shaft portion is within said energized inductor.

2. A method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft and an enlarged end, said end having a periphery with one transverse dimension substantially equal to or less than the largest transverse dimension of said shaft and another transverse dimension substantially greater than the largest v transverse dimension of said shaft, said method comprising: providing an inductor having a workpiece receiving opening generally matching the periphery of said end; providing a quenching unit aligned with said inductor and having a workpiece. passage large enough to allow passage of said enlarged end; heating said end with said inductor to a quench hardening temperature; moving said workpiece longitudinally until said end is past said inductor; then, rotating said workpiece about said axis; and, moving said workpiece longitudinally through said inductor and quenching unit to surface harden said workpiece.

3. A method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft and an enlarged end, said end having a periphery with ont transverse dimension substantially equal to or less than the largest transverse dimension of said shaft and another transverse dimension substantially greater than the largest transverse dimension of said shaft; said method comprising: providing an inductor having a workpiece receiving opening generally matching the periphery of said end; providing a quenching unit aligned with said inductor and having a workpiece passage large enough to allow passage of said enlarged end; supporting said workpiece stationary with said end within said inductor; energizing said. inductor to heat said stationary end to a quench hardening temperature; moving said workpiece longitudinally until said end is past said inductor; then, rotating said workpiece about said axis; and, moving said workpiece longitudinally through said inductor and quenching unit at a controlled rate to surface harden said workpiece. Y

4. A method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft having a diameter x and a terminal spade-shaped head having a first transverse dimension y and a second transverse dimension z with being substantially greater than x and z being substantially equal to or less than x, the method comprising the steps of: providing a generally rectangular inductor with an internal workpiece receiving opening having transverse dimensions of y+2K and y+2K with K and K being the normal air gap constants for spacing an inductor from a workpiece being inductively heated; providing a quenching unit below said inductor, supporting said head within said workpiece receiving opening of said inductor; energizing said inductor to heat said head; moving said workpiece axially from said inductor, through said quenching unit to quench said heated head; after said head moves from said inductor, rotating said workpiece on said longitudinal axis; and, then, progressively moving said rotating workpiece through said energized inductor and through said quenching unit to heat and quench harden progressively said head.

5. A method of surface hardening a steel workpiece with a longitudinal axis and comprising a shaft having a diameter x and a terminal spade-shaped head having a first transverse dimension y and a second transverse dimension z with y being substantially greater than x and z being substantially equal to or less than x, the method comprising the steps of: providing a generally rectangular inductor with an internal workpiece receiving opening having transverse dimensions of y-l-2K and x+2K with K and K being the normal air gap constants'for spacing an inductor from a workpiece being inductively heated; providing a quenching unit below said inductor; bringing said head into said workpiece receiving opening of said inductor; energizing said inductor to heat said head; after said head is heated to the hardening temperature, moving said workpiece axially from said inductor, through said quenching unit to quench said heated head; after said head substantially passes said quenching unit, rotating said workpiece on said longitudinal axis; and, then, progressively moving said rotating workpiece through said energized inductor and through said quenching unit to heat and quench harden progressively said shaft.

6. An apparatus for surface hardening a steel workpiece with a longitudinal axis and comprising a shaft portion and a spade-shaped portion, said apparatus comprising: an inductor having a workpiece receiving opening generally matching said spade-shaped portion; means for selectively energizing said inductor; a quenching unit with a workpiece receiving passage which will allow passage of said spade-shaped portion; means for selectively directing a quenching fluid from said quenching unit inwardly of said passage; means for aligning said spadeshaped portion with said opening; means for moving said workpiece successively through said opening and said passage; and means for rotating said workpiece about said axis only when said shaft portion is within said opening of said inductor.

7. An apparatus for surface hardening a steel workpiece with a longitudinal axis and comprising a shaft and an enlarged end, said end having a periphery with one transverse dimension substantially equal to or less than the largest transverse dimension of said shaft and another transverse dimension substantially greater than the largest transverse dimension of said shaft, said apparatus comprising: an inductor having a workpiece receiving opening generally matching the periphery of said end; a quenching unit having a workpiece passage aligned with said opening and large enough to allow passage of said enlarged end; said inductor and quenching unit forming a hardening station; means for supporting said workpiece in alignment with both said opening and said passage and with said enlarged end being initially adjacent said station and said shaft extending from said end and away from said station; means for rotating said workpiece about said longitudinal axis; means for moving said workpiece axially through said station; and, means for sequentially controlling said rotating and moving means, said control means including means for first causing said moving means to progress said end into said opening of said inductor, after said end is heated, causing said moving means to progress said end through at least a part of said passage, and then causing said moving means to progressively move said shaft through said opening and passage, and said control means also including means for activating said rotating means after said end passes from said opening.

8. An apparatus for surface hardening a steel workpiece with a longitudinal axis and comprising a shaft and an enlarged end, said end having a periphery with one transverse dimension substantially equal to or less than the largest transverse dimension of said shaft and another transverse dimension substantially greater than the largest transverse dimension of said shaft, said apparatus comprising: an inductor having a workpiece receiving opening generally match-ing the periphery of said end; a quenching unit having a workpiece passage aligned with said opening and large enough to allow passage of said enlarged end; said inductor and quenching unit forming a hardening station; first and second centers for supporting said work-piece with said axis of said workpiece aligned with said opening and said passage; a frame for supporting said centers whereby the centers may be moved in unison along a path coinciding with said axis; means for moving said centers in unison; means for rotating said workpiece about said axis; and, means for controlling said moving and rotating means, said controlling means including first means for actuating said moving means to move said end into said inductor open' ing and, then, progress said end through said opening and through said quenching unit, and second means for then actuating said rotating means to rotate said workpiece while said moving means moves said shaft progressively and successively through said opening and said passage.

9. An apparatus as defined in claim 8 wherein said first means includes means for momentarily holding said 9 workpiece stationary with said end within said opening until said end is inductively heated to the quench hardening temperature.

10. An apparatus as defined in claim 8 including means for causing fluid flow through said quenching unit onto said workpiece upon actuation of said rotating means.

11. An apparatus as defined in claim 8 including means for causing fluid flow through said quenching unit toward said axis upon actuation of said moving means by said first means.

References Cited UNITED STATES PATENTS Bushell et a1. 266-5 Brown 148-146 X Dreyfus 148-150 X Riegel 14815O X Fliezar et al 219--10.73 X

DAVID L. RECK, Primary Examiner. C. N. LOVELL, Assistant Examiner. 

1. A METHOD OF SURFACE HARDENING A STEEL WORKPIECE WITH A LONGITUDINAL AXIS AND COMPRISING A SHAFT PORTION AND A SPADE-SHAPED PORTION, SAID METHOD COMPRISING THE STEPS OF: PROVIDING AN INDUCTOR HAVING A WORKPIECE RECEIVING OPENING GENERALLY MATCHING SAID SPADE-SHAPED PORTION; PROVIDING A QUENCHING UNIT WITH A WORKPIECE RECEIVING PASSAGE WHICH WILL ALLOW PASSAGE OF SAID SPADESHAPED PORTION; MOVING SAID WORKPIECE SUCCESSIVELY 